The present invention relates to catalytic articles, emissions treatment systems including catalytic articles, and methods for reducing contaminants in exhaust gas streams. More specifically, the present invention is concerned with multi-component filters, systems and methods for their use with lean burn engines, including diesel engines and lean burn gasoline engines.
Operation of lean burn engines, e.g., diesel engines and lean burn gasoline engines, provide the user with excellent fuel economy, and have very low emissions of gas phase hydrocarbons and carbon monoxide due to their operation at high air/fuel ratios under fuel lean conditions. Diesel engines, in particular, also offer significant advantages over gasoline engines in terms of their durability, and their ability to generate high torque at low speed.
Diesel engine exhaust is a heterogeneous mixture that contains particulate emissions such as soot and gaseous emissions such as carbon monoxide, unburned or partially burned hydrocarbons, and nitrogen oxides (collectively referred to as NOx), but also condensed phase materials (liquids and solids) which constitute the so-called particulates or particulate matter. Catalyst compositions, often disposed on one or more monolithic substrates, are placed in engine exhaust systems to convert certain or all of these exhaust components to innocuous compounds. For example, diesel exhaust systems can contain one or more of a diesel oxidation catalyst, a soot filter and a catalyst for the reduction of NOx. These components are costly and take up considerable space on the vehicle.
Therefore, there is an ongoing need to improve the efficiency of exhaust treatment systems without increasing the size and complexity of such systems.